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In this paper, we propose a holographic zoom system based on two adjustable lenses. Different from the traditional holographic system, a digital conical lens and a liquid lens are used as the zoomable lenses. The liquid lens with large effective image aperture is designed and produced by a 3D printer. By mechanically controlling the curvature of the liquid-liquid surface, the focal length of the liquid lens can be changed easily. Compared with the other lenses, the conical lens has a larger focal depth. By encoding the phase information of the conical lens on the liquid crystal on silicon, the focal length and focal depth of the conical lens can be adjusted easily. The liquid lens and conical lens cooperate with each other so as to realize the high quality of holographic zoom projection. With such a system, the size and depth of the reconstructed image can be changed easily according to the requirement. Experimental results verify the feasibility of the proposed system.

In this paper, a method of speckle noise suppression for holographic zoom display based on layered-pixel-scanning (LPS) algorithm is proposed. Different from the traditional algorithm, the proposed method suppresses the speckle noise based on a new algorithm design and light source optimization. The LPS algorithm is designed to calculate the phase-only hologram of the 3D object. By extracting the initial complex hologram of the 3D object and scanning the hologram by pixel, the errors of the complex amplitude can be reduced as much as possible. Then a hologram subsampling method based on the LPS algorithm generated is proposed, so the scaling of the reproduced image can be achieved easily. At the same time, the pattern with different random phase is generated and loaded on the spatial light modulator so that the reconstructed light can be optimized. When the optimized light irradiates on the phase hologram of the object, the reconstructed image with suppressed speckle noise can be displayed. The experimental results show that the proposed method has an excellent reproduction effect. Moreover, the feasibility and unique advantages of the proposed method in the holographic augmented-reality display, zoom display and multi-plane display have been proved. We believe that this method can promote the application of the holographic display.

In this paper, a holographic display system with wide viewing area is proposed based on the effective area expansion of the SLM. The effective area of the SLM is calculated based on the viewing area characteristics and expanded by using two SLMs. Different from the traditional holographic system based on the parallel-arranged SLMs or curved-arranged SLMs, we calculate the effective areas of the SLMs and the effective hologram of the system can be generated based on the effective-viewing-area (EVA) algorithm. The proposed system uses a 4K SLM by seamlessly stitching the effective areas of two 2K SLMs. After the EVA is calculated, the size of the effective hologram is inversely calculated according to the EVA. So, the effective area of the hologram is increased, and the calculation of the wasted information is greatly decreased. With the proposed system, the reconstructed object with large viewing area can be realized. Moreover, the calculation time for generating the hologram is reduced significantly. Experimental results verify the feasibility of the proposed system. In the proposed system, the 2K SLMs are used as examples for splicing, when more high-performance SLMs are used, the viewing area will be further expanded, and the advantage of the calculation speed will be more obvious than the traditional splicing method. The proposed system can provide new references to the holographic display system based on multiple SLMs stitching.